2- Once the parent nodes loaded then on parent node expand (when user clicks to expand the parent node) need to load some other nodes as children of the this parent node by ajax request to a different json file.

In the beforeload event handler I still can't get the expanded node to know what URL to change to, could you please post some example code showing how to capture the node, and I think I need to access the tree store proxy URL config to change it (Ext.data.proxy.Ajax what I'm using).